a. Field of the Invention
This invention relates to a fire alarm system, and more particularly to a fire alarm system which is adapted to discriminate the conditions of a fire based on analog signals obtained upon detection of changes in the physical phenomena of the surroundings which are caused in relation with the occurrence of the fire.
b. Relevant Arts
As a known system which detects various physical changes peculiar to a fire for discriminating the conditions caused by the fire, there can be mentioned, for example, a system which is adapted to detect a smoke density and a gas concentration increased due to the fire, detect the characteristic relationship between the smoke density and the gas concentration and determine the fire based on the relationship. This relevant art is known from U.S. Pat. No. 4,316,184 issued on Feb. 16, 1982 and also known from U.S. Pat. No. 4,319,229 issued on Mar. 9, 1982.
The discrimination of the conventional system, however, depends only upon the slope obtained from the relationship between the two physical changes peculiar to a fire. Therefore, it is difficult to synthetically and surely judge real danger of the fire, and in case the fire conditions do not follow the preset characteristic curve, the determination of the fire will be inaccurate, causing a delay in the fire detection or a false alarming.